Utilization of a power take-off (PTO) shaft on equipment such a tractor or the like to power associated agricultural implements is commonly known in the industry. Typically, the PTO shaft is coupled to an output shaft which is selectively driven through mechanical gearing at standardized speeds of either 540 rpm or 1000 rpm. The PTO shaft is configured for connection to an implement which is also designed to be operated at either 540 rpm or 1000 rpm.
In order to avoid connecting to implements for operation at the wrong speed, a power take-off shaft is typically configured with a standard 13/8 inch diameter connection having six splines for connecting to 540 rpm implements, and/or 21-splines for connecting to 1000 rpm implements. Alternatively, some PTO shafts are configured with a standard 13/4 inch diameter connection having 20 splines for connecting to 1000 rpm implements having similarly configured coupling mechanisms.
Thus, in order to accommodate the requirements of a particular implement, it is necessary to provide a power take-off assembly which allows quick and easy conversion to the desired PTO shaft configuration and associated speed of operation.
Various mechanisms have been employed for converting to a desired PTO shaft configuration. Some prior art devices utilize interchangeable PTO shafts having six tooth or 21 tooth splines for accommodating the desired output speed, while other devices utilize a single reversible PTO shaft having six tooth and 21 tooth spline ends extending in opposite axial directions.
Such PTO shafts are often maintained in place by an external snap-ring configured to engage an interior bore of the output shaft. Other known PTO shafts are maintained in place by a flanged locking mechanism arranged externally of the output shaft to which the PTO shaft is coupled.
One disadvantage of the PTO shafts with connecting flanges is that the flange adds to the overall length of the power take-off unit. Such excess length may be unacceptable in view of standards imposed by the agricultural industry. The excess length of the PTO shaft can also create instability of a tractor because the resulting hitch connection to an implement effects the load on the front axle of the tractor. Moreover, it also tends to be tedious and time consuming to connect the flange to the output shaft by bolts or the like.
When snap-rings are used to connect the PTO shafts to the output shafts, special tools are required to interchange the PTO shaft, which tends to be cumbersome and time consuming. The location of the snap-rings may add to this difficulty because they are exposed to debris, especially in the dirt and mud-filled environment of a farming field, thus making it difficult to properly use the tools. In addition, the connection may not be secure enough to adequately retain the PTO shaft during high speed operation. As will be appreciated by those skilled in the art, the PTO shaft is subjected to axial forces during operation of the agricultural implement. Accordingly, the snap-rings used to releasably fasten the PTO shaft in place may have insufficient strength to retain the PTO shaft in place.
It therefore remains desirable to provide a simple, compact locking mechanism for quickly and securely connecting a desired PTO shaft to the output shaft.
Various efforts have also been undertaken to correlate the desired PTO shaft speed with the connection of the PTO shaft to the output shaft. One such device utilizes a reversible PTO shaft having different length splined end portions. In either orientation, the outer end portion is adapted for engagement with the implement for the selected speed, while the inner end portion positions a hydraulic valve to allow pressurized fluid to engage a clutch associated with the proper drive gear. Another such device utilizes interchangeable PTO shafts having different lengths for displacing a cammed shaft a desired amount, thereby actuating clutch shifting elements to selectively engage the proper drive gear.
These types of mechanisms tend to be rather complex, thus reducing the efficiency of shifting between the high and low gears, which may decrease the reliability of the mechanism over time and require excess maintenance. In addition, the complexity of these types of mechanisms can add to the overall size and length of the power take-off unit. It therefore remains desirable to provide a simple, compact mechanism which automatically shifts gears in response to interchanging the PTO shaft.